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Heat stress risk windows (flowering/fruit set)

Heat stress is not constant through the crop cycle. The impact depends heavily on timing, duration, and crop stage.

The same temperature event can be harmless at one stage and yield-limiting at another. The key is understanding when heat actually matters.

Why this matters

  • Flowering and early fruit set are yield-defining stages
  • Heat stress at this point reduces fruit number, not just size
  • Damage is often invisible at the time, showing later as poor set
  • Short periods of stress can have disproportionate impact

Key mechanisms

  • Reduced pollen viability → fewer fruits set
  • Increased respiration → less energy available for development
  • High transpiration demand → temporary water stress even under irrigation
  • Disrupted calcium movement → higher risk of fruit quality issues

Two key stress patterns:

  • High temperature + low RH → dehydration stress
  • High temperature + high RH → poor transpiration and calcium transport

Practical checks

  • Are daytime temperatures consistently above optimal for the crop?
  • Is RH dropping too low or staying too high during peak heat?
  • Is the crop showing signs of:
  • flower drop
  • uneven fruit set

  • soft or weak growth

  • Are irrigation intervals struggling to keep up with demand?

  • Is airflow sufficient across the canopy?

Actions that usually work

  • Prioritise stability over optimisation during flowering and fruit set
  • Maintain consistent irrigation timing (avoid peaks and troughs)
  • Use air movement to support transpiration
  • Avoid sudden changes in:
  • EC
  • feed strategy

  • irrigation volumes

  • Reduce additional stress (e.g. aggressive nutrition changes)

  • Moderate temperature where possible (venting, shading, airflow)

Common traps / misreads

  • Assuming visible stress is required — damage often occurs before symptoms appear
  • Overreacting to short spikes instead of focusing on duration of stress
  • Chasing temperature control but ignoring humidity and airflow balance
  • Increasing EC during heat, which can worsen plant stress
  • Trying to “correct” with inputs instead of stabilising the environment

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